A conventional display support device, as disclosed in Taiwanese Utility Model Patent Publication No. M393137, includes a support arm having first and second joint members, a display mounting seat rotatably inserted into the first joint member, an extension arm rotatably connected to the second joint member, and a fixing seat connected to the extension arm. However, the display mounting seat and the extension arm are easily moved with respect to the first and second joint members in the presence of an external force, thereby causing the display to deviate from a position required by a user. That is, the conventional display support device cannot precisely lock the position of the display as desired.